Axial flow fan

ABSTRACT

An axial flow fan includes an impeller rotatable about a central axis with a plurality of rotor vanes, a motor that drives the impeller, a base portion that supports the motor, a housing that includes an intake vent, an exhaust vent, and an inner peripheral surface surrounding the impeller and the motor, and a plurality of stator vanes that respectively connects the base portion and the housing, wherein the inner peripheral surface includes a first inner peripheral surface arranged to increase a distance from the central axis toward the intake vent or the exhaust vent in an axial direction, and a recess provided between the first inner peripheral surface and a stator vane included in the plurality of stator vanes and facing the first inner peripheral surface. Thus, airflow is allowed to smoothly pass through the housing, resulting in a decrease in noise generated in the fan.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an axial flow fan.

2. Description of the Related Art

FIG. 1 is a perspective view of a conventional axial flow fan 10. Theaxial flow fan 10 includes an outer frame 101, a plurality of statorvanes 102, and a base 103. The outer frame 101 is a hollow memberprovided with an intake vent and an exhaust vent. There is formed adiameter expanded part 101 a and there are disposed the stator vanes 102and the base 103 at the exhaust vent of the outer frame 101. The outerframe 101, the stator vanes 102, and the base 103 are integrally formedby injection molded resin.

In injection molding, one die is formed by combining two kinds of dieparts, namely, a fixed die part and a movable die part. Melted resin iscast into the die and then is cooled. Thereafter, the cooled andsolidified resin is taken out of the die. The outer frame 101, thestator vanes 102, and the base 103 are thereby formed as one member.

There are provided a plurality of seats 104 formed at parts where thediameter expanded part 101 a and the stator vanes 102 are respectivelyjoined. The seats 104 are positioned at blind portions when anintegrally molded component having the outer frame 101, the stator vanes102, and the base 103 is seen from a direction of being taken out of thedie. When air is exhausted from the exhaust vent and hits the seats 104,there arise problems of noise generation, as well as decreases in volumeof airflow and static pressure thereof.

SUMMARY OF THE INVENTION

Various preferred embodiments of the present invention provide an axialflow fan including an impeller that includes a plurality of rotor vanesand is rotatable about a central axis, a motor that rotary drives theimpeller, a base portion that supports the motor, a housing thatincludes an intake vent, an exhaust vent, and an inner peripheralsurface to surround the impeller and the motor, and a plurality ofstator vanes that respectively connects the base portion and thehousing, wherein the inner peripheral surface includes a first innerperipheral surface arranged to increase a distance from the central axistoward the intake vent or the exhaust vent in an axial direction, and arecess located between the first inner peripheral surface and one of theplurality of stator vanes and faces the first inner peripheral surface.

According to the above described configuration, airflow is allowed tosmoothly pass through the housing, resulting in a decrease in noisegenerated in the axial flow fan. Moreover, decreases can be prevented ina volume of airflow taken into or exhausted from the axial flow fan aswell as a static pressure thereof. Further, the housing can be moldedwith a smaller amount of resin, thereby achieving significant costreduction for manufacture of the axial flow fan.

The above and other features, elements, advantages and characteristicsof the present invention will become more apparent from the followingdetailed description of preferred embodiments thereof with reference tothe attached drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of a conventional axial flow fan.

FIG. 2 is a perspective view of an axial flow fan according to a firstpreferred embodiment of the present invention.

FIG. 3 is a plan view of the axial flow fan shown in FIG. 2, which isseen from an exhaust side thereof.

FIG. 4 is a cross sectional view of the axial flow fan shown in FIG. 2.

FIG. 5 is a cross sectional view of an axial flow fan according to afirst preferred modification of the present invention.

FIG. 6 is a cross sectional view of an axial flow fan according to asecond preferred modification of the present invention.

FIG. 7 is a cross sectional view of an axial flow fan according to asecond preferred embodiment of the present invention.

FIG. 8 is a cross sectional view of an axial flow fan according to athird preferred embodiment of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring to FIGS. 2 through 8, preferred embodiments of the presentinvention will be described in detail. It should be noted that in theexplanation of preferred embodiments of the present invention, whenpositional relationships among and orientations of the differentcomponents are described as being up/down or left/right, ultimatelypositional relationships and orientations that are in the drawings areindicated; positional relationships among and orientations of thecomponents once having been assembled into an actual device are notindicated. Meanwhile, in the following description, an axial directionindicates a direction parallel or substantially parallel to a rotationaxis, and a radial direction indicates a direction perpendicular orsubstantially perpendicular to the rotation axis.

FIGS. 2, 3, and 4 are respectively a perspective view, a plan view, anda cross sectional view of an axial flow fan 11 according to a firstpreferred embodiment of the present invention.

As shown in FIGS. 2, 3, and 4, the axial flow fan 11 preferably includesan impeller 12, a plurality of stator vanes 13, a motor portion 14, anda housing 18. The impeller 12 is preferably rotary driven about acentral axis 23 by the motor portion 14. The housing 18 is preferably ahollow member provided with an exhaust vent 41 and an intake vent 43.The stator vanes 13 are preferably disposed at the exhaust vent 41, andare formed integrally with the housing 18 by injection molded resin.Alternatively, the stator vanes 13 and the housing 18 may be integrallyformed by aluminum die-casting.

As shown in FIG. 4, the impeller 12 preferably includes a cup 21 in acapped and substantially cylindrical shape, and a plurality of rotorvanes 22. The rotor vanes 22 are preferably disposed on an outerperipheral surface of a cylindrical wall of the cup 21 so as to beequally spaced apart from each other in a circumferential directionaround the central axis 23. There is preferably fixed a rotor holder 121to an inner side of the cup 21. The rotor holder 121 is preferably acapped and substantially cylindrical member made of a magnetic material(such as a metal material). The rotor holder 121 preferably includes acylindrical inner peripheral surface to which a rotor magnet 31 in asubstantially annular shape is fixed. There is fixed by press fitting orthe like to a capped part of the rotor holder 121 a shaft 123 having asubstantially columnar shape.

As shown in FIG. 4, the motor portion 14 is preferably disposed in theimpeller 12 and includes a stator 141 (partially shown) and a circuitboard (not shown). The stator 141 radially preferably faces the rotormagnet 31 and is electrically connected to the circuit board. Thecircuit board and the stator 141 preferably receive electric currentsand control signals transmitted from an external power supply (notshown) through a plurality of lead wires (not shown). When the stator141 is supplied with an electric current, there is generated a magneticfield at the stator 141. Interaction between the magnetic fieldgenerated at the stator 141 and a magnetic field of the rotor magnet 31causes torque between the stator 141 and the rotor magnet 31. Suchtorque preferably rotary drives the impeller 12 about the central axis23 to cause airflow along the central axis 23. It should be noted that,in FIG. 4, air flows from the axially upper side to the axially lowerside (namely, from the intake vent 43 to the exhaust vent 41).

As shown in FIGS. 2, 3, and 4, the housing 18 has an outer frame 15 anda base portion 16. The outer frame 15 is preferably a hollow member in asubstantially square pole shape. In planar view, the outer frame 15preferably includes a substantially rectangular or substantiallycircular outline and an inner peripheral surface 40 in a substantiallycircular shape.

The inner peripheral surface 40 preferably includes intake-side firstinner peripheral surfaces 42 a respectively provided at four corners oralong an entire inner peripheral area thereof of the intake vent 43. Theintake-side first inner peripheral surfaces 42 a preferably are formedso as to gradually increase the radial distance between the central axis23 and the inner peripheral surface 40 toward the intake vent 43 in theaxial direction. Similarly, the inner peripheral surface 40 preferablyincludes exhaust-side first inner peripheral surfaces 42 b respectivelyprovided at four corners or along an entire inner peripheral areathereof of the exhaust vent 41 so as to gradually increase the radialdistance between the central axis 23 and the inner peripheral surface 40toward the exhaust vent 41 in the axial direction.

As shown in FIG. 4, the inner peripheral surface 40 preferably includesa second inner peripheral surface 45 formed to be substantially inparallel with the central axis 23. The second inner peripheral surface45 and the respective first inner peripheral surfaces 42 preferably aresmoothly continued to each other.

The base portion 16 is preferably a bottomed and substantiallycylindrical member and axially supports the motor portion 14. The baseportion 16 is preferably disposed in the outer frame 15 at the intakevent 43 in the axial direction. The base portion 16 preferably includesa surface, on the axially exhaust side, which is flush with respect toends 15 a of the outer frame 15 on the axially exhaust side.

As shown in FIGS. 2, 3, and 4, the stator vanes 13 are preferablydisposed between the inner peripheral surface 40 of the outer frame 15and the outer peripheral surface of the base portion 16 so as to beequally spaced apart from each other in the circumferential direction,thereby serving as connectors between the inner peripheral surface 40and the base portion 16. Each of the stator vanes 13 preferably includesa first edge 25, a second edge 26, a first surface 27, and a secondsurface 28. The first surface 27 and the second surface 28 arepreferably inclined with respect to the central axis 23, and the firstedge 25 is positioned on the intake side in the axial direction whilethe second edge 26 is positioned on the exhaust side thereof. The firstedge 25 is preferably formed to be positioned on the opposite side withrespect to the second edge 26 in a direction R of rotation of theimpeller 12. The first surface 27 is preferably oriented opposite to thedirection R of rotation of the impeller 12 so as to mainly receiveairflow which is generated by rotation of the impeller 12. It should benoted that the impeller 12 is rotated in the direction R of rotationclockwise about the central axis 23, as shown in FIG. 2. Further, eachof the stator vanes 13 preferably includes an axial cross section in avane shape with curved surfaces. According to such a configuration, anair circulative component generated by rotation of the impeller 12 istransformed to a component flowing along the central axis 23, resultingin an increase in static pressure of air.

Alternatively, the first and second surfaces 27 and 28 may be madeinclined with respect to the central axis 23 at a different angle, sothat airflow is oriented to an arbitrary direction (such as the radiallyoutward direction). The stator vanes 13 may be disposed not at theexhaust vent 41 but at the intake vent 43 in the axial direction. Inthis case, the second edge 26 is positioned on the opposite side withrespect to the first edge 25 in the direction R of rotation of theimpeller 12. Air is oriented by the stator vanes 13 and is taken intothe housing 18. Accordingly, reduced is noise generated by airflowhitting the inner peripheral surface 40 and the like.

As shown in FIGS. 2, 3, and 4, the plurality of stator vanes 13preferably include a plurality of first stator vanes 13A each of whichextends from the central axis 23 toward the corresponding exhaust-sidefirst inner peripheral surface 42 b. There is formed a recess 52 at apart where a first outer edge 53 of each of the first stator vanes 13Ais connected to the corresponding exhaust-side first inner peripheralsurface 42 b. The recess 52 is preferably a space surrounded by thefirst outer edge 53 and the corresponding exhaust-side first innerperipheral surface 42 b. In other words, an end of the first outer edge53 on the axially exhaust side radially faces the correspondingexhaust-side first inner peripheral surface 42 b with the recess 52interposed therebetween. On the other hand, an end of the first outeredge 53 on the axially intake side is connected to the second innerperipheral surface 45.

Such a configuration minimizes a volume of each of the seats which isformed at a connection between the first outer edge 53 and thecorresponding exhaust-side first inner peripheral surface 42 b.Therefore, airflow generated by rotation of the impeller 12 is allowedto smoothly pass in the vicinity of the respective connections. As aresult, reduced is noise generated by airflow hitting the connections.

In addition, as the volume of each of the seats is minimized, there issecured a space to arrange therein the impeller 12 within the housing18, thereby realizing increases in volume of airflow and static pressurethereof.

The volume of each of the seats, which is minimized, enables reductionin the amount of resin required for forming of the housing 18 (theamount of aluminum, aluminum alloy, or the like in the case of aluminumdie-casting). Therefore, reduction is realized in the cost of thematerial for the axial flow fan 11.

The end of the first outer edge 53 on the axially intake side ispreferably connected to a part 42 c having a minimized diameter on theexhaust-side first inner peripheral surface 42 b (more specifically, theend of the second inner peripheral surface 45 on the axially exhaustside). Accordingly, secured are strength of the connection between eachof the first stator vanes 13A and the inner peripheral surface 40 aswell as an inner diameter of the second inner peripheral surface 45. Itshould be noted that each of the first stator vanes 13A may be connectedto both the corresponding exhaust-side first inner peripheral surface 42b and the second inner peripheral surface 45 including the boundarytherebetween. Further, the second edges 26 of the first stator vanes 13are formed to be flush with respect to the ends 15 a of the outer frame15, thereby realizing prevention of an increase in size of the outerframe 15.

Described below is an axial flow fan 11A according to a first preferredmodification made to the first preferred embodiment of the presentinvention. FIG. 5 is a cross sectional view of the axial flow fan 11A.The element of the axial flow fan 11A identical to that of the axialflow fan 11 is denoted by the similar reference symbol, and descriptionthereof will omitted.

As shown in FIG. 5, the axial flow fan 11A preferably includes aplurality of first stator vanes 13B which are connected to therespective first inner peripheral surfaces 42. Similarly to the firststator vanes 13A, the first stator vanes 13B are preferably disposedbetween the base portion 16 and the inner peripheral surface 40 so as tobe equally spaced apart from each other in the circumferentialdirection.

There is formed a recess 52A on the axially exhaust side of a radiallyouter end of each of the first stator vanes 13B. The recess 52A ispreferably a space surrounded by a first outer edge 53 which is inparallel or substantially in parallel with the central axis 23, a secondouter edge 531 which is perpendicular or substantially perpendicular tothe first outer edge 53, and an exhaust-side first inner peripheralsurface 42 b. On the other hand, the radially outer end of each of thefirst stator vanes 13B is preferably connected on the axially intakeside thereof to the corresponding exhaust-side first inner peripheralsurface 42 b. According to such a configuration, the volume of the seatformed at the connection between the first stator vane 13B and the innerperipheral surface 40 is minimized. As a result, reduced is noisegenerated by airflow hitting the respective connections, and preventedare decreases in volume of airflow and static pressure thereof.

Each of the first stator vanes 13B preferably includes an end 13 a, onthe axially exhaust side, which is flush with respect to the ends 15 aof the outer frame 15. According to such a configuration, the axialdimension of the axial flow fan 11A is suppressed to realize reductionin size of the axial flow fan 11A.

Each of the first stator vanes 13B preferably includes an end 13 b, onthe axially intake side, which is flush with respect to parts (theboundaries between the second inner peripheral surface 45 and therespective exhaust-side first inner peripheral surfaces 42 b) having aminimized diameter on the exhaust-side first inner peripheral surfaces42 b. According to such a configuration, there is secured an adequatespace for disposing the impeller 12 in the housing 18. Airflow generatedby rotation of the impeller 12 is guided smoothly to the stator vanes13, and reduced is noise generated by airflow hitting the first statorvanes 13B. It should be noted that the radially outer end of each of thefirst stator vanes 13B may be connected to both the second innerperipheral surface 45 and the corresponding first inner peripheralsurface 42 including the boundary therebetween.

The first outer edge 53 and the second outer edge 531 may notnecessarily form an angle equal to 90 degrees, but may form an acuteangle or an obtuse angle. Further alternatively, the respective firststator vanes 13B may have such angles different from one another.

FIG. 6 is a cross sectional view of an axial flow fan 11B according to asecond preferred modification made to the first preferred embodiment ofthe present invention. The constituent of the axial flow fan 11Bidentical to that of the axial flow fan 11 or 11A is denoted by theidentical reference symbol, and description thereof will be omitted.

As shown in FIG. 6, the axial flow fan 11B preferably includes aplurality of first stator vanes 13C which are connected to therespective exhaust-side first inner peripheral surfaces 42 b. A radiallyouter end of each of the first stator vanes 13C is preferably connectedon the axially intake side thereof to the corresponding exhaust-sidefirst inner peripheral surface 42 b. On the other hand, there is formeda recess 52B at the radially outer end of the first stator vane 13C onthe axially exhaust side.

As illustrated in FIG. 6, a boundary 54 between the first outer edge 53and the end 13 a on the axially exhaust side is preferably chamfered.Similarly, a boundary 541 between the first outer edge 53 and the secondouter edge 531 is chamfered. Such a configuration reduces as much aspossible the volume of the seat formed at a boundary between the firststator vane 13C and the corresponding exhaust-side first innerperipheral surface 42 b. As a result, airflow is allowed to smoothlypass in the vicinity of the boundary 54 and the boundary 541 of each ofthe first stator vanes 13C. Alternatively, the boundary 54 or 541 may beformed as a surface in a C-letter shape.

The first outer edge 53 may be positioned radially inside or outside thesecond inner peripheral surface 45. The boundary 54 or 541 may bechamfered into a shape different from one another in the respectiverecesses 52B or the respective first stator vanes 13C.

FIG. 7 is a cross sectional view of an axial flow fan 11C according to asecond preferred embodiment of the present invention. The elements ofthe axial flow fan 11C that are substantially identical to those of theaxial flow fan 11, 11A, or 11B are denoted by identical referencesymbols, and the description thereof will be omitted.

As shown in FIG. 7, the axial flow fan 11C preferably includes aplurality of first stator vanes 13D which are connected to the outerframe 15 of the housing 16 at the exhaust-side first inner peripheralsurfaces 42 b, at the second inner peripheral surfaces 45, or at boththe exhaust-side first inner peripheral surfaces 42 b and the secondinner peripheral surfaces 45. On the other hand, there is provided arecess 52C at the radially outer end of the first stator vane 13D on theaxially exhaust side. The recess 52C is preferably arranged to overlapwith the corresponding exhaust-side first inner peripheral surface 42 band the first stator vanes 13D when the recess 52C is seen in the axialdirection.

As illustrated in FIG. 7, the recess 52C is preferably a spacesurrounded by a first outer edge 53C which is substantially angled withthe central axis 23, a second outer edge 531C which is perpendicular orsubstantially perpendicular to central axis 23, and an exhaust-sidefirst inner peripheral surface 42 b. On the other hand, a radiallyoutermost end of each of the first stator vanes 13D is preferablyconnected to the outer frame 15 at the exhaust-side first innerperipheral surfaces 42 b, at the second inner peripheral surfaces 45, orat both of the exhaust-side first inner peripheral surfaces 42 b and thesecond inner peripheral surfaces 45. According to such a configuration,the volume of the seat defined at the connection between the firststator vane 13D and the inner peripheral surface 40 is minimized. As aresult, noise generated by airflow hitting the respective connections isprevented, and decreases in volume of airflow and static pressurethereof are also prevented.

Each of the first stator vanes 13D preferably includes an end 13 a of athird outer edge 26C on the axially exhaust side, which is flush orsubstantially flush with respect to the ends 15 a of the outer frame 15.The third outer edge 26C is perpendicular or substantially perpendicularto the central axis. According to such a configuration, the axialdimension of the axial flow fan 11C is decreased to realize a reductionin size of the axial flow fan 11C.

Each of the first stator vanes 13D preferably includes an axially upperedge 25C which is angled with respect to the central axis 23. A radiallyoutermost portion of the axially upper edge 25C is angled upward withrespect to the axial direction. Further, a plurality of rotor vanes 22Cof the impeller 12 preferably includes an axially lower edge 12C whichis angled with respect to the central axis 23. A radially outermostportion of the axially lower edge 12C is inclined upward with respect tothe axial direction. According to such a configuration, an adequatespace to provide the impeller 12 in the housing 18 is secured. Airflowgenerated by rotation of the impeller 12 is guided smoothly to the firststator vanes 13D, and noise generated by airflow hitting the firststator vanes 13D is prevented and minimized.

The first outer edge 53C is preferably positioned further in the radialdirection than a radially outermost edge of the rotor vanes 22C of theimpeller 12. It should also be noted that the first outer edge 53C ofone first stator vane 13D may be arranged to have a different shape thanothers of the first stator vanes 13D, if so desired.

The first outer edge 53C and the second outer edge 531C preferablydefine an obtuse angle. However, this angle could also be changed to anangle equal to approximately 90 degrees or an acute angle if so desired.Further alternatively, the respective first stator vanes 13D may haveangles that are different from one another.

Each of the first stator vanes 13D also preferably includes a firstinner edge 54C and a second inner edge 532C. The first inner edge 54C issubstantially angled with respect to the central axis 23 and the secondinner edge 532C is preferably perpendicular or substantiallyperpendicular with respect to the central axis 23. The first inner edge54C and the second inner edge 532C are arranged to preferably define anobtuse angle. However, this angle could also be changed to an angleequal to approximately 90 degrees or an acute angle if so desired. Thefirst inner edge 54C and the second inner edge 532C are arranged todefine a second recess 521C together with an outer peripheral surface161 of the base portion 16. As a result, noise generated by airflowhitting the respective connections is prevented, and decreases in volumeof airflow and static pressure thereof are also prevented.

FIG. 8 is a cross sectional view of an axial flow fan 11D according to athird preferred embodiment of the present invention. The elements of theaxial flow fan 11D that are substantially identical to those of theaxial flow fan 11, 11A, 11B, or 11C are denoted by identical referencesymbols, and the description thereof will be omitted.

As shown in FIG. 8, the axial flow fan 11D preferably includes aplurality of stator vanes 13E which are connected to the respectiveexhaust-side first inner peripheral surfaces 42D. A radially outermostend of each of the stator vanes 13E is preferably connected to the outerframe 15 of the housing 16 at the exhaust-side first inner peripheralsurfaces 42 b, at the second inner peripheral surfaces 45, or at boththe exhaust-side first inner peripheral surfaces 42 b and the secondinner peripheral surfaces 45. On the other hand, a recess 52D isprovided at the radially outer end of the stator vane 13E on the axiallyexhaust side.

As illustrated in FIG. 8, a surface of a first outer edge 53D ispreferably curved or convex and arranged to be connected with a secondouter edge 531D that extends perpendicularly or substantiallyperpendicularly with respect to the central axis 23. Such aconfiguration reduces as much as possible the volume of the seat definedat a boundary between the stator vane 13E and the correspondingexhaust-side first inner peripheral surface 42D. Further, theexhaust-side first inner peripheral surface 42D is also preferablycurved or convex. As a result, airflow is allowed to smoothly pass inthe vicinity of the recess 52D.

Each of the stator vanes 13E preferably includes an axially upper edge25D which is angled with respect to the central axis 23. A radiallyoutermost portion of the axially upper edge 25D is angled upward withrespect to the axial direction. Further, a plurality of rotor vanes 22Dof the impeller 12 preferably includes an axially lower edge 12D whichis angled with respect to the central axis 23. A radially outermostportion of the axially lower edge 12D is angled upward with respect tothe axial direction. According to such a configuration, an adequatespace to provide the impeller 12 in the housing 18 is secured. Airflowgenerated by rotation of the impeller 12 is guided smoothly to thestator vanes 13E, and noise generated by airflow hitting the statorvanes 13E is prevented and minimized.

The first outer edge 53D is preferably positioned further in the radialdirection than a radially outermost edge of the rotor vanes 22D of theimpeller 12. It should also be noted that the first outer edge 53D ofone stator vane 13E may be arranged to have a different shape thanothers of the stator vanes 13E, if so desired.

Each of the stator vanes 13E also preferably includes a first inner edge54D and a second inner edge 532D. The first inner edge 54D is preferablycurved or convex and arranged to be connected with the second inner edge532D, which is preferably perpendicular or substantially perpendicularwith respect to the central axis 23. The first inner edge 54D and thesecond inner edge 532D are arranged to define a second recess 521Dtogether with an outer peripheral surface 162 of the base portion 16.Further, the outer peripheral surface 162 of the base portion 16 is alsopreferably curved or convex. As a result, noise generated by airflowhitting the respective connections is prevented, and decreases in volumeof airflow and static pressure thereof are also prevented.

Alternatively, the first stator vanes 13A, 13B, 13C, 13D, and 13Eaccording to the various preferred embodiments of the present inventionmay be provided on the axially intake side (that is, at the intake vent43). The axial flow fan may include more than one type of stator vanesselected from the first stator vanes 13A, 13B, 13C, 13D, and 13Eaccording to the various preferred embodiments of the present invention.Further, the radially outer end of each of the first stator vanes 13A,13B, 13C, 13D, and 13E may be connected to a part other than theexhaust-side first inner peripheral surface 42 b and 42D. Even in suchcases, airflow is allowed to smoothly pass in the vicinity of therespective stator vanes.

The intake-side first inner peripheral surfaces 42 a may have a shapedifferent from that of the exhaust-side first inner peripheral surfaces42 b and 42D. Further, the respective intake-side first inner peripheralsurfaces 42 a (or the respective exhaust-side first inner peripheralsurfaces 42 b and 42D) may have shapes different from one another at therespective corners, and may have distances from the central axis 23different from one another.

While the preferred embodiments and the preferred modifications of thepresent invention have been described above, the present invention isnot limited to the above cases. It is to be understood that variationsand modifications will be apparent to those skilled in the art withoutdeparting the scope and spirit of the present invention. The scope ofthe present invention, therefore, is to be determined solely by thefollowing claims.

1. An axial flow fan comprising: an impeller including a plurality ofrotor vanes and rotatable about a central axis; a motor portion arrangedto rotatingly drive the impeller; a base portion arranged to support themotor; a housing including an intake vent, an exhaust vent, and an innerperipheral surface surrounding the impeller and the motor portion; and aplurality of stator vanes arranged to respectively connect the baseportion and the housing; wherein the inner peripheral surface includes afirst inner peripheral surface arranged such that a distance between thecentral axis and the first inner peripheral surface increases toward theintake vent and the exhaust vent in an axial direction; among theplurality of stator vanes, a first stator vane is arranged torespectively connect the base portion and the first inner peripheralsurface, the first stator vane including a first outer edge, a secondouter edge, and a third outer edge; the first outer edge is arranged toface the first inner peripheral surface with a recess interposedtherebetween; the second outer edge and the third outer edge, both ofwhich are perpendicular or substantially perpendicular to the centralaxis, are connected with the first outer edge; a connecting point of thefirst outer edge and the second outer edge is arranged radially outsidean outermost edge of the impeller; and the first outer edge and thesecond outer edge are arranged to define an obtuse angle.
 2. The axialflow fan according to claim 1, wherein an axially upper edge of thefirst stator vane and an axially lower edge of the plurality of rotorvanes are arranged to be angled with respect to the directionperpendicular or substantially perpendicular to the central axis.
 3. Theaxial flow fan according to claim 1, wherein a radially outermostportion of an axially upper edge of the first stator vane and a radiallyoutermost portion of an axially lower edge of the plurality of rotorvanes are arranged to be angled upward with respect to the axialdirection.
 4. The axial flow fan according to claim 1, wherein the innerperipheral surface of the housing includes a second inner peripheralsurface arranged to be substantially parallel with the central axis. 5.The axial flow fan according to claim 4, wherein a distance between theinner peripheral surface and the central axis is shortest at a portionthereof between the second inner peripheral surface and the centralaxis.
 6. The axial flow fan according to claim 1, wherein the connectingpoint is arranged radially inside the first inner peripheral surface orthe second inner peripheral surface.
 7. The axial flow fan according toclaim 1, wherein the housing, the base portion, and the plurality ofstator vanes are defined by a single monolithic member.
 8. The axialflow fan according to claim 1, wherein each of the plurality of statorvanes includes an axial end flush with an axial end of the housing. 9.The axial flow fan according to claim 1, wherein the first outer edgeand the second outer edge are continuous with each other.
 10. The axialflow fan according to claim 1, wherein the first outer edge and thethird outer edge define an angled boundary with one another.
 11. Theaxial flow fan according to claim 1, wherein the first stator vanefurther includes a first inner edge and a second inner edge; the firstinner edge is arranged to face an outer peripheral surface of the baseportion with an additional recess interposed therebetween; the secondinner edge and the third outer edge, both of which are perpendicular orsubstantially perpendicular to the central axis, are connected with thefirst inner edge; and the first inner edge and the second inner edge arearranged to define an obtuse angle.
 12. The axial flow fan according toclaim 1, wherein the first outer edge includes a curved or convexsurface.
 13. The axial flow fan according to claim 1, wherein the firstinner peripheral surface includes a curved or convex surface arranged todirectly oppose the curved or convex surface of the first outer edge.14. An axial flow fan comprising: an impeller including a plurality ofrotor vanes and rotatable about a central axis; a motor portion arrangedto rotatingly drive the impeller; a base portion arranged to support themotor; a housing including an intake vent, an exhaust vent, and an innerperipheral surface surrounding the impeller and the motor portion; and aplurality of stator vanes arranged to respectively connect the baseportion and the housing; wherein the inner peripheral surface includes afirst inner peripheral surface arranged such that a distance between thecentral axis and the first inner peripheral surface increases toward theintake vent and the exhaust vent in an axial direction; among theplurality of stator vanes, a first stator vane is arranged torespectively connect the base portion and the first inner peripheralsurface, the first stator vane including a first outer edge, a secondouter edge, and a third outer edge; the first outer edge is arranged toface the first inner peripheral surface with a recess interposedtherebetween; the second outer edge and the third outer edge, both ofwhich are perpendicular or substantially perpendicular to the centralaxis, are connected with the first outer edge; a connecting point of thefirst outer edge and the second outer edge is arranged radially outsidean outermost edge of the impeller; and the first outer edge includes acurved or convex surface.
 15. The axial flow fan according to claim 14,wherein an axially upper edge of the first stator vane and an axiallylower edge of the plurality of rotor vanes are arranged to be angledwith respect to the direction perpendicular or substantiallyperpendicular to the central axis.
 16. The axial flow fan according toclaim 14, wherein the inner peripheral surface of the housing includes asecond inner peripheral surface substantially parallel with the centralaxis.
 17. The axial flow fan according to claim 16, wherein a distancebetween the inner peripheral surface and the central axis is shortest ata portion thereof between the second inner peripheral surface and thecentral axis.
 18. The axial flow fan according to claim 14, wherein thefirst outer edge is arranged radially inside the first inner peripheralsurface or the second inner peripheral surface.
 19. The axial flow fanaccording to claim 14, wherein the housing, the base portion, and theplurality of stator vanes are defined by a single monolithic member. 20.The axial flow fan according to claim 14, wherein each of the pluralityof stator vanes includes an axial end flush with an axial end of thehousing.
 21. The axial flow fan according to claim 14, wherein the firstouter edge and the second outer edge are continuous with each other. 22.The axial flow fan according to claim 14, wherein the first stator vanefurther includes a first inner edge and a second inner edge; the firstinner edge is arranged to face an outer peripheral surface of the baseportion with an additional recess interposed therebetween; the secondinner edge and the third outer edge, both of which are perpendicular orsubstantially perpendicular to the central axis, are connected with thefirst inner edge; and the first inner edge and the second inner edge arearranged to define an obtuse angle with respect to the directionperpendicular or substantially perpendicular to the central axis. 23.The axial flow fan according to claim 14, wherein the first innerperipheral surface includes a curved or convex surface arranged todirectly oppose the curved or convex surface of the first outer edge.24. The axial flow fan according to claim 14, wherein the first innerperipheral surface includes a curved or convex surface arranged todirectly oppose the curved or convex surface of the first outer edge.